MANILA: A Philippine offensive against the extremist Abu Sayyaf group after a spate of kidnappings has left 18 soldiers and five fighters dead in the worst violence in the troubled south this year, authorities said Sunday.

Saturday’s clashes on the strife-torn island of Basilan came after an April 8 ransom deadline set by Abu Sayyaf, who had threatened to behead some of their foreign hostages.

At least four soldiers were beheaded in the fighting, which involved about a hundred Abu Sayyaf, regional military spokesman Major Filemon Tan said.

“This is part of the military operations against the Abu Sayyaf,” launched after a series of abductions of foreigners, he told reporters.

Another military spokesman said the soldiers were on their way to attack an Abu Sayyaf hideout when they were ambushed.

“Our group was heading to attack them. On the way, they were ambushed,” Colonel Benedict Manquiquis, spokesman for the unit involved in the battle, told radio station dzRH.

“The enemy had the high ground so no matter where our soldiers fled to seek cover, they could still be hit by the heavy firepower and improvised explosive devices of the members of the Abu Sayyaf group,” he said.

Tan said 53 soldiers and about 20 Abu Sayyaf had also been wounded in the violence but he did not give details.

The clash came shortly after a retired Italian priest being held hostage by the Abu Sayyaf was freed on Friday.

Last month, the Abu Sayyaf posted a video to their Facebook page in which a Norwegian and two Canadian hostages said they would be killed if the ransom was not paid.

While the ransom amount was not specified, the militants in an earlier video demanded P1 billion ($21 million) for each of the three foreigners.

Since the April 8 ransom deadline passed there has been no word on the hostages’ fate.

The Abu Sayyaf is a small group of militants known for kidnapping foreigners and demanding huge ransoms.

Eighteen other foreign hostages are being held in the Philippines, most or all of them thought to be in the hands of the Abu Sayyaf.

The group was established in the early 1990s with seed money from Osama bin Laden’s Al Qaeda network.

It has been blamed for the country’s worst terror attacks, including a 2004 Manila Bay ferry bombing that claimed 116 lives.

Its leaders have in recent years pledged allegiance to the Islamic State group that controls vast swathes of Iraq and Syria.

They are based in the southern islands of Basilan and Jolo which both have large Muslim populations.

Various Muslim separatist insurgencies in the southern Philippines have claimed more than 100,000 lives since the 1970s. AFP